Fully coupled hydromechanical model for compacted soils

To accomplish a proper conception and further modeling of the mechanical behavior of soils, observations at the micro and macro scales need to be merged. The authors believe that the link between scales can be achieved using the effective stress concept. In this paper, we present a model that quantifies the air and water volumes contained within the pores of a solid when their pore pressure is varied. The macroscopic consequences of this are expressed in terms of a single stress that is used to formulate a simple elastoplastic constitutive model to predict volume strains and shear strength of soils.     

Spread of water along clay strata in dry soils

Moscow. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 121–125, September–October, 1988.     

Collapse failure in dry clay soils caused by tine implements

The relation between forces applied to the soil and the resultant soil reaction was studied in dry clay soils under a quasi-static condition. As a tine advanced in dry compact clay soils at 5.2% dry basis moisture content, masses of soil collapsed one by one in front of the tine. The horizontal and vertical components of soil resistance measured were cyclic and in phase, with distinct peak and trough values. The peak values and trough values indicated the soil stress conditions before and immediately after each failure occurred. The frequency of failure depended on the size of the tine. The magnitude of the peak values depended on level of compaction and trough values on density of collapsed mass. The paper presents the details of observations.     

Pulverization characteristics of clay soil

Soil pulverization and failures during chip formation using rotating simple wedge-shaped blades for microsite preparation were analyzed to determine soil cutting characteristics. Equations were developed for soil bite size and blade projected area, and a new term was proposed relating the power requirement for rotating the pulverizer blade to the power required for penetrating the soil profile. The results of this study indicated that the rotational power requirements, in general, increased with increases in rotational and downward speeds, and the penetration power was slightly affected by the rotational speeds and was very small in comparison with the rotational power. The soil bite size appeared to play a great role in identifying the power requirements of a pulverizer blade. A substantial increase in rotational power requirement at the same rotational speeds was required due to increases in bite sizes; this increase might be due to the increases in soil-blade friction forces. During soil pulverization, chip dimensions were affected by the operational speeds, soil strength, blade geometry, and number of pulverizer blades. The pulverizer shaft diameter has little influence on the total power requirements but definitely affects the soil packing sequence of the planting cycle when the soil pulverizer for microsite preparation is incorporated into the planting head. An example illustrating the use of the data presented in this study is included to assist in the selection and sizing of a soil pulverizer's power unit.     

A dynamic equation for the pressure-sinkage relationship in saturated clay soils

Experiments showed that the plate pressure-sinkage relationship in a saturated clay soil was strongly dependent on deformation rate. An equation for the pressure-sinkage relationship incorporating deformation rate was developed, using visco-plastic theory, and was found to describe the measured data well.     

Shrinking–swelling phenomenon of clay soils attributed to capillary-crack network

The shrinking and swelling behavior of clay soil is modeled by considering a capillary-crack network, the hydraulic conductivity of which is accounted for by the network tortuosity and specific crack length tracing a horizontal cross-section. Retention curve is determined by the total crack volume and volume of water filled cracks. Available data on hydraulic conductivity for two clay soils are compared with predictions and the agreements is good.     

Slip-line field solution for ultimate bearing capacity of a pipeline on clay soils

A slip-line field solution is presented for the ultimate bearing capacity of the pipeline on a purely-cohesive clay soil, taking into account of circular configuration of the pipe, the pipe embedment, and the pipe-soil interfacial cohesion. The derived bearing capacity factors for a smooth rigid pipe may degenerate into those for the conventional rectangular-shaped strip footing while the pipe embedment approaches zero. Parametric studies indicate that, the pipe-soil interfacial properties have much influence on the bearing capacity for the pipe foundation on clayedy soils.     

Statistical characteristics of the pressure fluctuation in a hydraulic jump

The author examines experimental data on the correlation in an essentially inhomogeneous, statistically stationary pressure fluctuation field at the bottom of a turbulent flow in the region of a hydraulic jump. Certain data relating to other statistical characteristics of the field in question (in particular, the one-dimensional distribution laws) may be found in [1].The author thanks O. F. Vasil'ev for supervising this research and also V. A. L'vov, N. S. Poleshchuk, and V. V. Zykov for making and adjusting the apparatus for analyzing the oscillograms, and Z. V. Danilov for compiling the programs and processing the experimental data.     

Implicit scheme for integrating constitutive model of unsaturated soils with coupling hydraulic and mechanical behavior

A constitutive model of unsaturated soils with coupling capillary hystere- sis and skeleton deformation is developed and implemented in a fully coupled transient hydro-mechanical finite-element model （computer code U-DYSAC2）. The obtained re- sults are compared with experimental results, showing that the proposed constitutive model can simulate the main mechanical and hydraulic behavior of unsaturated soils in a unified framework. The non-lineaxity of the soil-water characteristic relation is treated in a similar way of elastoplasticity. Two constitutive relations axe integrated by an implicit return-mapping scheme similar to that developed for saturated soils. A consistent tan- gential modulus is derived to preserve the asymptotic rate of the quadratic convergence of Newton＇s iteration. Combined with the integration of the constitutive model, a complete finite-element formulation of coupling hydro-mechanical problems for unsaturated soils is presented. A number of practical problems with different given initial and boundary conditions are analyzed to illustrate the performance and capabilities of the finite-element model.     

水硬性石灰合成及拉破坏特性试验研究

水硬性石灰在欧洲石质文物修复和加固中获得了很大成功。我国的石质文物主要是砂岩,水硬性石灰的修复效果不好。为满足我国石质文物修复和加固的需求,本文以石灰石和黏土为原料,在950℃煅烧不同时间,制备出水硬性石,对试样的成分、微观形貌、收缩率、抗拉强度和拉破坏过程等进行了研究。结果表明:(1)试样中含有水硬性成分2CaO·SiO2(C2S);煅烧8h时,成分与欧洲水硬性石灰NHL5接近;1.5CaO·SiO2·xH2O(C-S-H)和CaCO3的含量随龄期的增加逐渐增加。(2)龄期1~3d,收缩率较小;龄期4~6d,收缩率以线性规律增加;7d以后,收缩率趋于稳定。(3)局部变形区随拉应力的增加而变大,邻近局部变形区逐渐合并,形成面积更大的应变局部化带;载荷超过峰值后,产生微裂隙;随载荷进一步增加,微裂隙扩展,贯穿整个试件,发展成宏观裂隙,使试件破坏。(4)抗拉强度随龄期的增加而增加,水硬性石灰中C-S-H、CaCO3等相互交织,构成空间致密体,使试件力学强度提高。合成的水硬性石灰物理力学性能与欧洲水硬性石灰NHL5相近,并且成分均匀、可控,在石质文物修复和加固工程中具有良好应用前景。     

锥阀附近水力特性的三维数值模拟研究

采用可压缩的两相流模型,辅以Realizable k-ε湍流模型来模拟锥阀附近的水流水力特性,对于自由水面的处理采用了VOF法。通过对计算的压力场以及流线的分析,指出锥阀在水力消能中的作用。数值模拟结果与试验资料的比较分析表明两者吻合较好,从而验证了该模型在锥阀湍流模拟中的可靠性。     

Effect of animal drawn puddling implements on hydraulic conductivity of lateritic sandy clay loam soil in West Bengal, India

To determine out the suitable animal drawn puddling implement in terms of reduction in hydraulic conductivity of soils were investigated in this research study. In rice (Oriza sativa L.) cultivation in West Bengal, India, reduction in hydraulic conductivity of soil facilitates better rice growth. To determine, the effect of puddling implements, i.e., an animal drawn rotary puddler (I₁), a 3-tine tiller (I₂) and a local plough (I₃), and number of passes of the implements on hydraulic conductivity of the puddled as well as the non-puddled layer of a lateritic sandy clay loam with respect to relative age (i.e., elapsed time after puddling operation) was studied under controlled soil-bin conditions. It was concluded that the hydraulic conductivity of soil decreases with the number of passes and relative age. A mathematical model was developed for calculating the hydraulic conductivity of puddled soil layer. It was concluded that the hydraulic conductivity obtained with the rotary puddler was 2.27 times less than that with the 3-tine tiller and 3.09 times that with local plough after the fifth pass of puddling operations.